@lain if you kill (premeditated etc etc) 1 person vs 100 people the same general result happens: you go to prison, family/etc will disown you, you lose the life you previously had.
if i were at a breaking point and wanted to kill (to any feds reading this, im not) i would rather kill a LOT of people. wouldnt really be worth throwing away my life only killing one CEO or politician, thats not going to change the world.
neither does shooting up a church or gay club, but to the broken mind it makes more sense. the only people whod justify one-off killings are those whod get away with it. as such, gang violence consists of these and make up most of the gun violence numbers.

not to say CIA would never be involved in mass shooting shenanigans. they could also be involved in singular assassinations of threats (jfk, epstein, boeing guys).